The present invention relates to a recording apparatus, and more particularly to a non-impact recording apparatus.
Conventionally, a non-impact recording method is known, in which a counter electrode uniformly covered with a toner powder is disposed adjacent a recording electrode with a predetermined gap therebetween and a sheet-like or ribbon-like recording material is placed in the gap and the counter electrode is moved with the above-mentioned gap maintained while applying an image signal to the recording electrode and, at the same time, the recording material is moved, whereby a toner image corresponding to the applied image signal is formed on the surface of the recording material.
Referring to FIG. 1, there is shown a recording apparatus adopting such a recording method. In FIG. 1, a recording electrode 1 is shown as used in a receiving recorder of a facsimile system. The recording electrode 1 is a long and narrow plate extending perpendicularly to the plane of FIG. 1, and in the lower longitudinal end of the recording electrode 1, there are embedded multiple stylus electrodes. The respective ends of the multiple stylus electrodes are lined up with a very small space therebetween and in accordance with an image signal to be recorded, a potential is applied to a certain combination of the stylus electrodes.
As the recording electrode, a pin tube and a letter pattern can be employed as well.
In this conventional apparatus, a counter electrode 2 is shaped like a drum and is disposed axially parallel to the longitudinal axis of the recording electrode 1, with a predetermined gap maintained between the lower longitudinal end surface of the recording electrode 1 and the peripheral surface of the counter electrode 2, and the recording electrode 1 extends so as to cover the full length of the counter electrode 2.
The counter electrode 2 is rotatable in the direction of the arrow, and is rotated in the direction of the arrow with toner T held on the peripheral surface of the counter electrode 2 when image recording is made.
Recording material S is non-conductive and is transported in the direction of the arrow by a transporting system (not shown) during the image recording step. When the leading edge of the recording material S enters the gap between the recording electrode 1 and the counter electrode 2, this apparatus becomes ready for recording.
As the recording material, ordinary paper with an insulating film can be used. The recording material is shaped like a sheet or a ribbon. The ribbon-like recording material is not always narrow.
Powder toner T is conductive and magnetic and is attracted to the peripheral surface of the counter electrode 2 by a magnetic force of a magnet disposed inside the counter electrode 2. As the toner, a non-magnetic toner can be employed. However, the magnetic toner is more suitable for this recording apparatus since the magnetic toner can be easily supplied to the counter electrode 2. The use of a conductive toner is more advantageous than that of a toner with a high resistivity since it is unnecessary to charge the toner electrically during the image recording process.
When the recording apparatus is ready for recording, the back side of the recording material S is brought into contact with the stylus electrode embedded end surface of the recording electrode 1, while the front side of the recording material S is in light contact with or extremely close to the toner T deposited on the counter electrode 2.
In this condition, an image signal is applied to the recording electrode 1 and, at the same time, the recording material S is transported in the direction of the arrow at a predetermined speed and in synchronism with the transportation of the recording material S, the counter electrode 2 is rotated in the direction of the arrow.
In the gap between the recording electrode 1 and the counter electrode 2, namely in the recording portion of the apparatus, an electric field is formed locally in the direction perpendicular to the direction of movement of the non-conductive recording material S through the recording portion in accordance with an applied signal voltage. By the action of this electric field, the toner T on the counter electrode 2 is electrically charged. The toner T is then selectively transferred to the surface of the recording material S by the mutual action of the electric charge of the toner T and the above-mentioned electric field, in accordance with an image signal, whereby a toner image is formed on the recording material S. Therefore, when this toner image is fixed to the recording material S by some subsequent means, the image recording is completed.
In the case where a pin tube is employed as the recording electrode 1, an electric charge is applied to the back side of the recording material S in accordance with the image signal and the toner T is attracted to the recording material S by the mutual action of the charge applied to the recording material S and an electric charge induced electrostatically on the toner T. Thus, even in the case where the above-mentioned recording electrode 1 is employed, it is possible to perform recording by electrically charging the recording material S.
However, this recording system has the following potential problems. First, during the recording process, on one occasion, the toner layer on the counter electrode 2 may be brought into contact with the recording material S and on another occasion, the toner layer may be out of contact with the recording material S. This has some adverse effects on the image recording, which make the image density of a recording image ununiform and make it difficult to obtain a recording image with a high resolution. Furthermore, by the physical contact of the surface of the recording material S with the toner layer, a considerable background is caused in the recording image.
Such a background can be eliminated to some extent by differing the transportation speed of the recording material S from the moving speed of the toner T. In this case, however, it becomes difficult to obtain a recording image with a high image density.
In the case where a magnetic toner is employed, since a magnetic pole of the magnet for holding the toner T on the peripheral surface of the counter electrode 2 is located adjacent the recording portion, the toner T deposited on the recording material S for image formation is partly attracted back to the counter electrode 2 by the magnetic force of the magnet disposed inside the counter electrode 2. In order to prevent this, it is necessary to lengthen the application time of the pulse image signal in accordance with the width of a recording area. This countermeasure, however, give a limitation to the speedup of recording.